Chronic back problems cause pain and disability for a large segment of the population. In many cases, chronic back problems are caused by intervertebral disc disease. When an intervertebral disc is diseased, the vertebrae between which the disc is positioned may be inadequately supported, resulting in persistent pain. Stabilization and/or arthrodesis of the intervertebral joint can reduce the pain and debilitating effects associated with disc disease.
Spinal stabilization systems and procedures have been developed to stabilize diseased intervertebral joints and, in some cases, to fuse the vertebrae that are adjacent the diseased joint space. Most fusion techniques include removing some or all of the disc material from the affected joint, and stabilizing the joint by inserting an implant (e.g., a bone graft or other material to facilitate fusion of the vertebrae) in the cleaned intervertebral space.
Spinal implants can be inserted into the intervertebral space through an anterior approach, a posterior approach, or postero-lateral approach. The anterior approach involves a surgeon seeking access to the spine through the front (i.e., abdominal area) of the patient. The posterior approach involves a surgeon seeking access to the spine through the back of the patient. The postero-lateral approach is similar to the posterior approach with access coming more from either or both sides of the patient. A variety of different anterior, posterior and postero-lateral techniques are known.
It is often an advantage to use the posterior approach because such an approach typically involves a smaller and less intrusive opening than those required by anterior approach techniques. Because a posterior approach involves a smaller opening, two or more implants are often used in this approach as compared to using a single larger implant. For example, in one technique, adjacent vertebral bodies are stabilized by implanting separate implants between the vertebral bodies on opposite sides of a sagittal plane passing through the midline of the vertebral bodies. When using multiple implants to support adjacent vertebrae, it is desirable for the implants to have similar or identical mechanical properties so that uniform support is provided on both sides of the sagittal plane. In some instances, it also is desirable for the implants to have similar or identical biologic properties (e.g., to reduce the risk of tissue rejection and to enhance the uniformity of creeping substitution).